Our laboratory has a long-standing interest in understanding bi-directional signaling events that take place at the APC/T-lymphocyte interface and involves The T-cell receptor as well as co-receptors such as SLAM (Signaling Lymphocyte Activation Molecule). The function of SLAM and SLAM related receptors in T -and B lymphocytes has been the subject of intensive research, but practically nothing is known of the function of these receptors in dendritic cells, the most efficient antigen presenting cells. In this proposal we plan to investigate the function of SLAM and Slam-related (SLAM-rel) cell surface receptors in dendritic cells. The expression level of SLAM-family receptors, EAT-2 (a small adaptor protein that associates with SLAM-rel), and selected members of the Src-kinase family of tyrosine kinases will be determined in monocyte derived dendritic cells, using the combination of flow cytometry, quantitative RT-PCR and western blot analysis. Next, we will test the hypothesis that EAT-2 regulates proximal signal transduction events initiated by SLAM-family of cell surface receptors in mature dendritic cells. These studies will include molecular dissection of ternary and multi-protein signal complexes associated with SLAM/SLAM-rel by immunoprecipitation studies. The interaction of EAT-2 with Src-kinases and SLAM/SLAM-rel and the effect of this interaction on SLAM phosphorylation signaling will be analyzed in detail by yeast two hybrid analysis and immunoprecipitation. Lastly, we designed in vitro experiments to evaluate the effect of SLAM/SLAM-rel signaling on the APC function of dendritic cells, in particular on the priming and polarization of naive CD4+ T lymphocytes into Th1 -or Th2-type effector cells. The in vivo significance of SLAM signaling in dendritic cells is underscored by the finding that SLAM is the "real" receptor for the measles virus. Deregulation of SLAM signaling in dendritic cells was suggested to mediate the strong immunosuppressive effect characteristic of measles. Completion of the proposed studies should significantly improve our understanding the role SLAM plays in the regulation of Th1/Th2 balance by dendritic cells, which may improve the clinical management of a wide range of diseases including allergic and autoimmune disorders, bacterial, and parasitic infections.